Conventionally, as a wavelength selection switch used in optical wavelength multiplex communication, for instance, as described in Patent Document 1 and Patent Document 2, a device including input/output ports configured by at least one input port and at least one output port, a dispersion element, a light collecting element and a deflector is known.
For instance, a wavelength selection switch described in Patent Document 1 is configured as illustrated in a top view in FIG. 44. The wavelength selection switch includes a plurality of input/output ports 1110, a microlens array 1111, a light collecting lens 1112, a dispersion element 1113, a light collecting element (light collecting mirror) 1114, a deflection prism 1115, and a deflector 1116. FIG. 45 is a side view developing and illustrating the wavelength selection switch along an optical path. In FIG. 45, the dispersion element 1113, which is actually a reflection type, is illustrated by a form of a transmission-type dispersion element, and the light collecting element 1114 of the reflection type is illustrated by a form of a lens. A signal luminous flux made incident from one of the input/output ports 1110 is collected at a primary light collecting point P through the light collecting lens 1112, then advances while diverging, is turned into a parallel luminous flux by the light collecting element 1114, and is dispersed in an x direction (in FIG. 45, a direction vertical to a paper surface) in the dispersion element 1113. The light of a prescribed wavelength of the dispersed signal light is collected to a deflection element 1117 corresponding to the prescribed wavelength of the deflector 1116 by the light collecting element 1114. The deflection element 1117 deflects the incident light of the prescribed wavelength in an array direction (y direction) of the input/output ports 1110. Thus, the light of the prescribed wavelength of the signal light is emitted from a prescribed input/output port 1110 through respective optical elements in an order opposite to the time of incidence.